1. Field of the Invention
The present invention relates to a developing apparatus used in an image forming apparatus. The image forming apparatus utilizes an electrophotographic process or an electrostatic recording process, such as a copying machine, a printer, or a facsimile apparatus. The present invention also relates to an image forming apparatus equipped with the developing apparatus. More specifically, the present invention relates to a developing apparatus that uses a two-component developer including a toner and a carrier, and an image forming apparatus equipped with the same.
2. Description of the Related Art
Conventionally, in an image forming apparatus utilizing, for example, an electrophotographic process, a developing apparatus performing development with a two-component developer having a mixture including a toner and a carrier is widely used. In particular, from the viewpoint of image color tint, etc., many developing apparatuses for color image forming apparatuses use a two-component developer.
In a developing apparatus using a two-component developer, a toner is consumed through a developing operation, and a new toner is supplied in an amount corresponding to a consumption amount. On the other hand, a carrier remains in a developer container (developer vessel) without being consumed. Thus, the carrier, which is agitated together with the toner, is deteriorated through agitation. Deterioration of the carrier occurs when the toner adheres to a carrier surface layer. The toner adheres to a carrier surface layer typically as a result of friction when the developer is agitated and compression at the time of passing through a gap between a developer bearing member (such as a developing roller) provided in the developer container and a developer layer thickness regulating member (such as a regulating blade). When the carrier deteriorates, charging performance of the developer deteriorates. This results in deterioration in developing performance, which leads to generation of defective images. Therefore, the carrier is periodically replaced.
Replacement of the carrier is performed in the following manner. The developer is extracted via a developer extraction port provided in the developer container, and the developing apparatus is filled with a new developer. During the replacement, the toner, which is a powder, may be scattered, and soils the image forming apparatus and the periphery thereof.
In this regard, Japanese Patent Publication No. 2-21591 discusses a developing apparatus that suppresses deterioration of a developer, so that there is no need to perform a special developer replacing operation. Such a developing apparatus adopts a system generally referred to as a trickling system. In the trickling system, a discharge port is provided at a predetermined height on a housing side wall of the developing apparatus. To maintain a property of the developer at a fixed level, the discharge port in the developing apparatus is utilized to successively discharge an excess developer in the developing apparatus, which results from the supply of a developer including a toner and a carrier.
More specifically, in this method, an amount of the developer in the developer container increases due to the supply and any excess developer corresponding to an amount over a height of the discharge port overflows and is discharged from the discharge port.
However, in the trickling system, a conveyance member provided at a position facing the developer discharge port splashes the developer, with the result that the developer is discharged to an unnecessary degree.
Japanese Patent Application Laid-Open No. 2005-208338 discusses a developing apparatus has a configuration in which a cutout is provided in a screw of a conveyance and agitating member at a portion thereof facing a developer discharge port. According to this configuration, the developer is not easily affected by a splashing effect of the screw, and the developer can be discharged in a stable manner.
However, in the configuration in which the cutout is provided in the screw facing the developer discharge port or in the vicinity thereof as in the developing apparatus discussed in Japanese Patent Application Laid-Open No. 2005-208338, the following problem is involved. Usually, taking into account manufacturing variation in components and thermal deformation thereof, the developer container and the conveyance member are incorporated in the apparatus with some play. As a result, a relative position between the conveyance member and the developer container may vary within a range of the above described play. Due to the variation corresponding to the above described play, variation in positions of the cutout of the screw and of the developer discharge port in an axial direction may be generated. When such variation is generated, the discharge characteristics will fluctuate from apparatus to apparatus.